Laboratory for Molecular Pharmacology, Department of Biomedical Sciences, and Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Nørre Allé 14, 2200, Copenhagen, Denmark.
Laboratory for Molecular Pharmacology, Department of Biomedical Sciences, and Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Nørre Allé 14, 2200, Copenhagen, Denmark.
Mol Metab. 2018 Jun;12:62-75. doi: 10.1016/j.molmet.2018.03.016. Epub 2018 Apr 3.
G protein-coupled receptors (GPCRs) act as transmembrane molecular sensors of neurotransmitters, hormones, nutrients, and metabolites. Because unmyelinated vagal afferents richly innervate the gastrointestinal mucosa, gut-derived molecules may directly modulate the activity of vagal afferents through GPCRs. However, the types of GPCRs expressed in vagal afferents are largely unknown. Here, we determined the expression profile of all GPCRs expressed in vagal afferents of the mouse, with a special emphasis on those innervating the gastrointestinal tract.
Using a combination of high-throughput quantitative PCR, RNA sequencing, and in situ hybridization, we systematically quantified GPCRs expressed in vagal unmyelinated Na1.8-expressing afferents.
GPCRs for gut hormones that were the most enriched in Na1.8-expressing vagal unmyelinated afferents included NTSR1, NPY2R, CCK1R, and to a lesser extent, GLP1R, but not GHSR and GIPR. Interestingly, both GLP1R and NPY2R were coexpressed with CCK1R. In contrast, NTSR1 was coexpressed with GPR65, a marker preferentially enriched in intestinal mucosal afferents. Only few microbiome-derived metabolite sensors such as GPR35 and, to a lesser extent, GPR119 and CaSR were identified in the Na1.8-expressing vagal afferents. GPCRs involved in lipid sensing and inflammation (e.g. CB1R, CYSLTR2, PTGER4), and neurotransmitters signaling (CHRM4, DRD2, CRHR2) were also highly enriched in Na1.8-expressing neurons. Finally, we identified 21 orphan GPCRs with unknown functions in vagal afferents.
Overall, this study provides a comprehensive description of GPCR-dependent sensing mechanisms in vagal afferents, including novel coexpression patterns, and conceivably coaction of key receptors for gut-derived molecules involved in gut-brain communication.
G 蛋白偶联受体（GPCR）作为神经递质、激素、营养物质和代谢物的跨膜分子感受器。由于无髓鞘的迷走传入神经丰富地支配胃肠道黏膜，肠道来源的分子可能通过 GPCR 直接调节迷走传入神经的活性。然而，迷走传入神经中表达的 GPCR 类型在很大程度上尚不清楚。在这里，我们确定了小鼠迷走传入神经中表达的所有 GPCR 的表达谱，特别强调了那些支配胃肠道的 GPCR。
我们采用高通量定量 PCR、RNA 测序和原位杂交相结合的方法，系统地定量了迷走无髓鞘 Na1.8 表达传入神经中表达的 GPCR。
在 Na1.8 表达的迷走无髓鞘传入神经中最丰富的肠道激素 GPCR 包括 NTSR1、NPY2R、CCK1R，在较小程度上还包括 GLP1R，但不包括 GHSR 和 GIPR。有趣的是，GLP1R 和 NPY2R 与 CCK1R 共表达。相比之下，NTSR1 与 GPR65 共表达，GPR65 是肠道黏膜传入神经中优先富集的标志物。仅在 Na1.8 表达的迷走传入神经中发现了少数微生物衍生代谢物传感器，如 GPR35，在较小程度上还包括 GPR119 和 CaSR。参与脂质感知和炎症的 GPCR（如 CB1R、CYSLTR2、PTGER4）以及神经递质信号转导（CHRM4、DRD2、CRHR2）在 Na1.8 表达神经元中也高度富集。最后，我们在迷走传入神经中鉴定了 21 种具有未知功能的孤儿 GPCR。
总的来说，这项研究提供了迷走传入神经中 GPCR 依赖性传感机制的全面描述，包括新的共表达模式，以及可能涉及参与肠-脑通讯的肠道来源分子的关键受体的协同作用。
